[PATCH 1/3] x86: Add GLIBC_ABI_GNU2_TLS version dependency

Tue Aug 19 18:35:50 GMT 2025

On Mon, Aug 18, 2025 at 1:13 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Linux/x86, programs and shared libraries compiled with
> -mtls-dialect=gnu2 may fail silently at run-time against glibc without
> the GNU2 TLS run-time fixes for:
>
> https://sourceware.org/bugzilla/show_bug.cgi?id=31501
> https://sourceware.org/bugzilla/show_bug.cgi?id=31372
>
> A version tag, GLIBC_ABI_GNU2_TLS, has been added to glibc to indicate
> that glibc has the working GNU2 TLS run-time.  Add the --gnu2-tls-tag
> option to i386/x86-64 ELF linker to add the GLIBC_ABI_GNU2_TLS version
> dependency in output programs and shared libraries when linking against
> glibc if input relocatable object files have R_386_TLS_DESC_CALL or
> R_X86_64_TLSDESC_CALL relocation.  The output will fail to load and run
> at run-time against glibc which doesn't define the GLIBC_ABI_GNU2_TLS
> version.
>
> Add the --enable-gnu2-tls-tag configure option to enable --gnu2-tls-tag
> by default.  If unspecified, linker will add the GLIBC_ABI_GNU2_TLS
> version dependency if input object files have R_386_TLS_DESC_CALL or
> R_X86_64_TLSDESC_CALL relocation and libc.so defines the GLIBC_ABI_GNU2_TLS
> version.
>
> Update elf_link_add_glibc_verneed to properly add the GLIBC_2.36 version
> dependency when -z mark-plt -z nopack-relative-relocs passed to x86-64
> ELF linker.
>
> bfd/
>
>         PR ld/33130
>         * elf-bfd.h (_bfd_elf_link_add_glibc_version_dependency): Add
>         a pointer to bool argument.
>         * elf-linker-x86.h (elf_linker_x86_params): Add
>         gnu2_tls_version_tag.
>         * elf32-i386.c (elf_i386_scan_relocs): Set has_tls_desc_call to
>         1 for R_386_TLS_DESC_CALL.
>         (elf_i386_add_glibc_version_dependency): New.  Undef before
>         FreeBSD support.
>         * elf64-x86-64.c (elf_x86_64_scan_relocs): Set has_tls_desc_call
>         to 1 for R_X86_64_TLSDESC_CALL.
>         (elf_x86_64_add_glibc_version_dependency): Add GLIBC_ABI_GNU2_TLS
>         version dependency if GLIBC_ABI_GNU2_TLS dependency isn't disabled
>         and has_tlsdesc_call isn't 0.

Small update to use  for x32.  Also use elf_x86_64_add_glibc_version_dependency
for x32.

>         * elflink.c (elf_link_add_glibc_verneed): Changed to return bool.
>         Remove the pointer to elf_find_verdep_info argument.  Add a
>         pointer to bool argument, auto_version. Return true if linked
>         against glibc.  Otherwise return false.  If the version dependency
>         is added, set *auto_version to true.  If *auto_version is true,
>         add the version dependency only if libc.so defines the version.
>         (_bfd_elf_link_add_glibc_version_dependency): Add a pointer to
>         bool argument and pass it to elf_link_add_glibc_verneed.
>         (_bfd_elf_link_add_dt_relr_dependency): Pass NULL to
>         _bfd_elf_link_add_glibc_version_dependency.
>         (elf_backend_add_glibc_version_dependency): Undef before CloudABI
>         support.
>         * elfxx-x86.h (elf_x86_link_hash_table): Add has_tls_desc_call.
>
> ld/
>
>         PR ld/33130
>         * NEWS: Mention --gnu2-tls-tag, --no-gnu2-tls-tag and
>         --enable-gnu2-tls-tag.
>         * config.in: Regenerated.
>         * configure: Likewise.
>         * configure.ac: Add --enable-gnu2-tls-tag.
>         * ld.texi: Document --gnu2-tls-tag/--no-gnu2-tls-tag.
>         * ldlex.h (option_values): Add OPTION_GNU2_TLS_VERSION_TAG and
>         OPTION_NO_GNU2_TLS_VERSION_TAG.
>         * emulparams/elf32_x86_64.sh (EXTRA_EM_FILE): Changed to
>         "elf-x86-64-glibc".
>         * emulparams/elf_i386.sh (EXTRA_EM_FILE): Set to "elf-i386-glibc".
>         * emulparams/elf_i386_fbsd.sh (EXTRA_EM_FILE): New.  Set to
>         "elf-x86".
>         * emulparams/elf_i386_haiku.sh (EXTRA_EM_FILE): Likewise.
>         * emulparams/elf_x86_64.sh (EXTRA_EM_FILE): Likewise.
>         * emulparams/elf_x86_64_cloudabi.sh (EXTRA_EM_FILE): New.  Set
>         to "elf-x86-64".
>         * emulparams/elf_x86_64_fbsd.sh (EXTRA_EM_FILE): Likewise.
>         * emulparams/elf_x86_64_haiku.sh (EXTRA_EM_FILE): Likewise.
>         * (EXTRA_EM_FILE): Likewise.
>         * (EXTRA_EM_FILE): Likewise.
>         * emultempl/elf-i386-glibc.em: New file.
>         * emultempl/elf-x86-64-glibc.em: Likewise.
>         * emultempl/elf-x86-64.em: Likewise.
>         * emultempl/elf-x86-glibc.em: Likewise.
>         * emultempl/elf-x86.em (elf_x86_64_before_parse): Removed.
>         (LDEMUL_BEFORE_PARSE): Likewise.
>         (elf_x86_64_before_allocation): Likewise.
>         (LDEMUL_BEFORE_ALLOCATION): Likewise.
>         * emultempl/solaris2-x86-64.em: New file.
>         * testsuite/ld-i386/gnu2-tls-1.s: Likewise.
>         * testsuite/ld-i386/gnu2-tls-1a.rd: Likewise.
>         * testsuite/ld-i386/gnu2-tls-1b.rd: Likewise.
>         * testsuite/ld-x86-64/gnu2-tls-1.s: Likewise.
>         * testsuite/ld-x86-64/gnu2-tls-1a.rd: Likewise.
>         * testsuite/ld-x86-64/gnu2-tls-1b.rd: Likewise.
>         * testsuite/ld-x86-64/mark-plt-2.rd: Likewise.
>         * testsuite/ld-x86-64/mark-plt-2.s: Likewise.
>         * testsuite/ld-i386/i386.exp: Run GLIBC_ABI_GNU2_TLS tests.
>         * testsuite/ld-x86-64/x86-64.exp: Likewise.
>

-- 
H.J.
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